500hp 6.5L Diesel Race Engine

Revenge Of The GM IDI

500 Hp!
In the January '09 issue of Diesel Power we showed you Heath Diesel's 6.5L-powered Chevy pickup ("This 6.5L Chevy Runs 153 mph"), which could outrun most Corvettes. The article highlighted the truck's Bonneville land speed racing buildup, but there was so much reader interest in the motor, Bill Heath agreed to let us publish his GM indirect-injection (IDI) engine building secrets. While these modifications may not be for everyone (or every truck), they should help readers looking to narrow the gap between '82 to '99 GM diesels and '01 to '11 Duramax trucks.

A Near-Stock Combination
Heath Diesel's land speed race engine wasn't stock by any means, but it did use a lot of factory engine components. Heath's buildup began with a Scat Enterprises cast-steel 6.5L crankshaft bolted into the block with a Heath Diesel main stud kit.

Based on Heath Diesel's experience, the 6.2L piston design is thought to be superior to that of the 6.5L piston. The 6.2L part is heavier, features a more robust wristpin boss, a heavier crown, and a lower placement of the rings. These are differences that play a role in the more extreme applications such as land speed racing.

Engine Block
Heath Diesel cleaned the 6.2L block using a three-step process that included hot tanking, sandblasting, and acid etching. Then engine block filler was poured into the coolant passages with the main bearing caps torqued in place. Heath added the filler until it was 5/8 inch below the engine's deck surface. This improved the structure, while still allowing the necessary coolant circulation between the block and the cylinder heads. As soon as the first side was poured, Heath Diesel worked fast to install a cylinder head with a used gasket and the fasteners used in the final assembly. When the first side of the engine had firmed up, Heath Diesel rotated the block and filled the other side. The engine was then allowed to sit for more than 60 days to allow the block filler to fully cure.

Machine Work and Rotating Assembly
The block was delivered to Joe's Grinding in Yakima, Washington, for the necessary machine work. Owner Rich Eims thoroughly examined the block and checked the main bearing housing bores and alignment. He also made sure the decks were square and parallel to the crankshaft centerline. The block was bored and honed with the main bearing caps in place and a BJH deck plate was installed with a used head gasket torqued in place. Mahle recommended that its 6.2L pistons (PN 027481) were fitted to the individual cylinders with a skirt clearance of 0.0025 inch. Because Heath's engine operates at higher combustion temperatures and engine speeds, it was decided the clearance should be set at 0.0033 inch. To help achieve this finished clearance, Tech Line PowerKote DFL-1 coating was applied to the piston skirts to help fill in the irregularities of the cylinder walls.

Bored Not Honed
Heath Diesel believes reconditioning the connecting rods is critical when building a quality 6.2L or 6.5L. After checking for any cracks, the rods were outfitted with new bolts and properly resized on both ends. An important part of this process was to ensure the proper finishing and accurate sizing of the wristpin bushing bore. After fitting each connecting rod with a new wristpin, the pin bushings were finish-sized to the correct internal dimension and the bore centerline was made perfectly parallel.

For best performance and durability, the pin bushings were bored to dimension-not honed. Heath Diesel is convinced that these pin bushings cannot be successfully honed to size (the accepted automotive practice) because the honing stones will load with the relatively soft material and cause a coarse and deeply scratched load-bearing surface-one that will imbed hone-stone material. These gouges cause point-contact-welding and lubrication breakdown failure between the pin and bushing. The diameter of the bushing is then too large to provide the necessary contact surface area.

22.5:1 Compression Ratio and Cylinder Head Secrets
The race engine ran a 22.5:1 static compression ratio. In addition, Heath force fed it with 30 psi of boost while spinning at 5,000 rpm. The piston deck clearance (height above the gasket surface) was 0.006 inch. A standard-thickness (0.044 inch compressed) Fel-Pro head gasket was used in conjunction with the 0.006-inch deck clearance to achieve a piston-to-cylinder head squish clearance of about 0.038 inch, minus piston rocking.

Over the years, Heath has determined a specific procedure for fastening the heads onto the block when using head studs. Cleanliness is critical, so both sealing surfaces were wiped using acetone prior to assembly. Before installing Fel-Pro head gaskets on the locating dowels, Heath coated them with Permatex Copper Coat gasket sealer. After the heads were set on the block, each stud was installed after applying Permatex Ultra Grey to the coarse-thread end of the stud. The studs have to be sealed, as they screw into the water jackets. The threads were loaded to their major diameter with sealer-no more, no less.

They were then run into the block and fully seated before being backed off an eighth of a turn. When all of the studs were installed, a little brush was used to coat the threads with ARP's special lube. Next, on went ARP washers, which are lubed on both surfaces. Then the nuts were run up and down by hand. This last step was intended to distribute the lube onto the threads of both the stud and the nut in order to assure the lowest friction when tightening them up. Next, and per the factory torque sequence, the ARP nuts were torqued to 25 ft-lb. The torque was increased in 10-pound increments till it was at 115 ft-lb. Then the engine was allowed to sit overnight, and each stud was retorqued again to 115 ft-lb.

Factory Intake|
Heath left the intake and cylinder head ports untouched because the original intake runner is a pretty decent design in terms of flow and swirl-generating quality. Turbulence during the combustion process helps ensure oxygen reaches the greatest number of fuel particles.

New Cam and Old Timing Drive
In previous engines, Heath used the factory camshaft, but this engine uses a cam designed to enhance power output at 4,000 to 4,500 rpm, where the engine spends the majority of its time.

The Heath Diesel race engine used the stock timing sprockets and chain versus an aftermarket arrangement. According to Heath, these pieces are bulletproof and work great. The specified looseness of the chain is 0.5 inch for new parts and 0.8 inch as the service limit. In 2008, Heath Diesel raced with a timing chain that had been in service for 288,000 miles and had 0.6 inch of free play.

Lubrication System
Heath's next race engine will be outfitted with a standard-volume original-equipment Melling oil pump, factory pump pickup, and oil pan. The later-model, higher-volume 6.5L oil pump does not work well in this application because it will suck the pan dry and oversupply the engine's upper regions. In normal pickup truck rpm ranges, it works fine. Heath is also reworking the rocker arms to reduce oil flow into the rocker arm chambers. The factory upper engine oiling is a little too free flowing for the land speed engine.

Heath Diesel runs its race engine without an oil cooler by making some changes in the bypass valves. In fact, Heath would like to have a far greater oil temperature at the start of the run but is limited to only being able to idle the engine while in the staging lanes. "I would much prefer being able to do our full-throttle pass right at the end of a 30-mile highway drive," Bill said. Oil temperature at the end of the pass is still not very high, at least not high enough to warrant oil cooling. Heath used a full synthetic 5W-30 oil designed for gasoline applications. "Our oil does not need to be able to deal with soot accumulations, as we don't drive it more than about 1,000 miles between engine dismantle and inspection," he explained. The lightweight oil is used to reduce power loss.

Fuel Injection System
The limit on power imposed by the 6.5L's comparatively fuel-stingy Stanadyne DS-4 injection pump is a very real one and Heath knew the only hope was to squeeze every last bit of power from what fuel it does provide. The Heath Diesel IDI engine used the off-the-shelf HO Bosch fuel injectors. These were combined with factory high-pressure lines and a new Stanadyne 5521 injection pump. The only modification to the injection pump was the addition of Tim Outland's Feed the Beast fuel inlet fittings. Heath runs an AirDog fuel lift pump adjusted to 7 psi of fuel pressure. The higher engine speed substantially changed the amount of fuel necessary, which began to stretch the limits of the regular heavy-duty lift pump.

The 6.5L racer was outfitted with one of Heath Diesel's PMD Isolator systems as well as the latest version of GM's electronic filter harness. The truck featured a modified version of the Max E Tork GL4 program. This tune was custom-engineered for this unique application. It was set up to allow the engine to operate at a maximum speed of 5,000 rpm. This differs from the version Heath Diesel offers its customers, which only has a limit of 3,700 rpm. Its injection timing schedule was altered to suit the particular engine speed, and it also data logs engine information. The maximum fuel rate is identical to the regular production program, which exercises the injection pump to its physical limits. The primary limiting factor in this combination is the DS-4 Stanadyne injection pump. However, in consideration of this limit, the team is very satisfied with the power.

Water Injection to the Max
Heath fed a more-than-normal amount of pure water to the engine with a version of the Heath Water-Mist Injection system. During a run across the salt, the engine consumed 0.65 gallons of diesel, and 1.1 gallons of water. The intake air temperature stayed very close to 130 degrees and exhaust gas temperature hovered in the 1,350-to-1,400-degree range.

See It Run: Bonneville 2010
"We will have our pit area set up and the truck inspected in time for opening ceremonies on Saturday morning-August 14th 2010-at the Bonneville Salt Flats in northwestern Utah," Bill said. "We are joined there each year by a growing number of loyal supporters who, as honorary salt brethren, jump right in to lend a hand and to make these outings successful. Diesel Power readers, you are hereby invited to join in the festivities!"